river, northeastern Iceland, fed by the northern meltwaters of the Vatna Glacier in east-central Iceland; it flows northward for 128 miles (206 km) to Axar Fjord, an arm of the Greenland Sea. The river skirts the eastern margins of Ódádhahraun, an extensive lava field, and then tumbles over a series of falls, the largest of which (Dettifoss (Detti Falls), 144 feet 【44 m】) has the greatest hydroelectric potential on the island. The second longest of Iceland's rivers, Jökulsá á Fjöllum has the largest drainage basin, 3,070 square miles (7,950 square km).